The invention relates to the regulation of alternators. The invention provides improved control of alternators which utilize a sleeve for shunting and regulation of the rotor magnetic flux. Frink, in U.S. Pat. No. 4,027,229, discloses a regulatable permanent magnet alternator having a sleeve that is shiftable through 90 electrical degrees by means of a motor. The output of the alternator may be regulated between maximum and minimum values by so shifting the sleeve. The sleeve position is fixed during operation of the Frink alternator. The motor is connected by bolts through a plate to the sleeve. As taught by Frink, the sleeve need only rotate through 90 electrical degrees, i.e., an angle equal to one-half of the pole separation angle in order to shift the alternator between its minimum output condition and its maximum output condition. However, the sleeve is not adapted to be rotated during operation of the alternator.